Membraneless micro fuel cells shown in Fig. 1[1] have eliminated some technical issues related to membrane-based fuel cells such as dry-out at anode and flooding at cathode. However, performance of membraneless micro fuel cell using dissolved oxygen as oxidant is mainly restricted by low concentration of oxygen which can not provide sufficient driving force to replenish depletion boundary layer at electrode surfaces. Consequently, electro-catalytic activity on cathode is weak (see Fig. 2 [2]). The goal of this work is to manipulate depletion boundary layer to minimize mass transfer limitation on electrodes. Chemical activity limitation on cathode can be addressed by (1) using high oxygen concentration as oxidant [3], (2) using three stream laminar flows [4], and (3) using multiple inlets or outlets [5]. A new design by combing multiple inlets or outlets with tapered electrode channel is proposed and studied in this work. Computational simulation will be performed to report improved performance with various design configurations in terms of fuel utilization in variation with flow rate. With conventional micro fuel cell (Fig. 1), fuel utilization has agreed well with experiments [1]. Significance of results is to provide design rules – evidence to promote clean micro power source.